Electric furnace.



PATENTED DEC. 20, 1904.

H. M. HOWE.

ELECTRIC FURNACE.

APPLICATION FILED OOT.3.1902.

N0 MODEL.

iNVENTOR:

HEY/WM. WW5,

HIS ATTORNEYS,

UNITED STATES Patented. December 20, 1904.

PATENT OEEIcE.

HENRY M. I-IOWVE, OF NEWV YORK, N. Y., ASSIGNOR TO EIMER AND AMEND,

' OF NEW YORK, N. Y., A CORPORATION OF NEl V YORK.

ELECTRIC FURNACE.

SPECIFICATION forming part of Letters Patent No. 778,194, dated December20, 1904,

Application filed October 3, 1902. Serial No 125,780.

To all whom it nutjr concern:

Be it known that LHENRY M. HOWE, a citi- Zen of the United States ofAmerica, residing in the city of New York, county of New York, and Stateof New York, have invented new and useful Improvements in ElectricFurnaces, of which the following is aspecitication. The main object ofmy invention is to construct a simple, cheap, and efficient electric oresistance-furnace more especially adapted for laboratory, dental, andother uses, as for determining melting-points of metals, calibratingthermo-electric couples by means of the melting-point of copper,determining the cooling curves of steel, or for use for any chem.- icalor physical operation when it is desired to reach quickly and accuratelya desired temperature or to hold an object for a long time at a giventemperature, and especially when it is desirable to do so in anatmosphere free from the products of combustion of any fuel or in anyspecial atmosphere.

In the accompanying drawings, Figure 1 is a vertical section of 'myimproved furnace. Fig. 2 is a plan on the line 2 2, Fig. 1; and Fig. 3is a detached view of a means for use in putting the heating-coil intoplace.

The furnace itself may conveniently consist of two semieylinders ofmagnesia A A, holo lowed to form the heating-chamber and provided with acover of magnesia B B and a stopper C, also of magnesia, which isperforated to admit the leads :0 3 of a thermo-electric couple. Thefurnace is heated by the spiral of platinum or other suitable wire D D,(entering and departing by the openings I and K,) through which acurrent of any desired strength is passed, bringing it to incandescenceand to any desired temperature not above the melting-point of theheating-wire. The

crucible E, which is surrounded by the heating-coil, is also preferablyof magnesia.

It is not necessary that the magnesia of which the furnace is madeshould be abso lutely pure. That which I have used has the followingcomposition: silica, two per cent, (determined accuratelyg) ferric oXidand alumina, one per cent, (determined approximately;) lime, two percent, (determined apl proximately;) magnesia, ninety-five per cent, 5

(by difference.)

Magnesia may be diluted with a certain amount of lime; but the amountshould not be very great, because of the tendency of the lime to slake,and the less lime the better. The presence of any large amount of silicais objectionable.

I have heard of some unsuccessful attempts with furnaces of this generalclass and have attributed these failures to the use of siliceous 6omaterials for the furnace-walls. Of course such a result is what weshould expect, since the silica would readily be electrolyzed by thecurrent and the resultant silicon would alloy with platinum and destroyit; but the magnesia furnace here described is free from this objection.It has been used successfully in laboratory-work in my laboratory, andtemperatures up to 1,100 centigrade have been developed in it overconsiderable periods of time. Indeed, it has been held near 1,400centigrade for about two hours without indication of any deteriorationof the platinum.

Great care should be taken not to turn on an excessive amount ofcurrent, because this is liable to melt the platinum. The current shouldbe controlled carefully with an ammeter and a differential rheostat. henbeginning to use the furnace, the operator should first turn on thecurrent slowly till the wire begins to glow. Then, setting thethermoelectric junction of the pyrometer in place and closing thefurnace, he should increase the current very slowly and cautiously, soas to learn just what current is required to produce 8 5 within thefurnace the temperature which he needs.

In the illustration Fig. 1, F F are a pair of steel disks boundtogether, but separated by the inverted thermojunction N of the thermo-0 electric pyrometer. This arrangement permits the observation andrecord of retardations in the heating and cooling of F F in other words,the determinations of the cooling curves of steel-a purpose for whichthe 9 5 furnace is well adapted, as well as for the tie termination ofmelting-points. In calibrating thermo-electric couples by means of themelting-point of copper this apparatus permits the crucible to be filledwith an atmosphere composed of equal volumes of carbonic acid andcarbonic oxid, a gaseous mixture which does not oxidize copper and atthe same time is unlikely to cause deposition of carbon. In such anoperation the mixture of carbonic acid and oxid, or any other desiredatmosphere, is introduced through a pipe H, which, as well as theopenings I and K, may be tightly packed, while the cover (3 is luted on.Absolutely air-tight closure, however, is not required, since thegas-pressure through I-I sufficient to maintain a plenum in the crucibleand to offset small leakages will be a sufficient prevention of changeof the interior atmosphere. As already observed, the parts A A, B B, andC are of magnesia. L indicates packing.

In order to increase its radiating-surface, the spiral D may be made offlattened wire, and preferably of the special U-shaped section shown, sothat it may be the better adapted to the groove, while giving a largeheatingsurface.

To facilitate placing the spiral I) in its groove M, molded within thefurnace-walls, I devised the mandrel Gr. (Shown in Fig. 3.)

, The mandrel, with the wire wound upon it,

is set approximately in place in the furnace. The mandrel is thenwithdrawn by screwing it to the left. The two halves of the furnace areat the same time pushed together, and the wire is thus fitted into thespiral groove made for that purpose in the inner faces of thefurnace-walls. The metallic conductor thus laid in the spiral groove inthe chamber constitutes a large part of the interior wall of theheating-chamber instead of being on the outside of the wall, as iscommon, so that the 3. An electric resistance-furnace, having a spiralgroove in the inner face of the walls of the heating-chamber and aheating-wire of U-section laid in said groove.

4. An electric resistance, having a spiral groove formed in the innerface of the walls of the heating-chamber and the heating-wire laid insaid groove, as and for the purpose de-- scribed.

5. An electric resistance-furnace, having aspiral groove formed in theinner face of the walls of the heating-chamber, and a heatingwire laidin said groove with a crucible to [it into said chamber, substantiallyas described.

6. An electric furnace consisting of two in ternally-grooved bloc-ks anda cover with a plug therein, in combination with a resistance element inthe grooves of the blocks.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

HENRY M. HOIVE. Nitnesses:

MILTFOR Bisnor, LLOYD BAKER.

